Visible crew/equipment: At the end of the movie, when Captain America and Black Widow are walking towards the camera to train the new Avengers, the reflection of the cameraman's feet are seen on the glass railings in the back as they walk backwards shooting the actors.
Factual error: After the Scarlet Witch forces Banner to become Hulk, he goes berserk in Johannesburg, South Africa. A few minutes earlier they were near the ocean at a ship scrap yard. Johannesburg is many kilometres away from any ocean.
Tony Stark: What's the vibranium for?
Ultron: I'm glad you asked that, because I wanted to take this time to explain my evil plan.
Trivia: Stan Lee makes his customary appearance whilst the Avengers and a load of War Veterans are enjoying a get together. Thor offers a 1,000 year old Asgardian drink to Captain America, and Stan Lee asks for some. (00:25:15)
Question: Why is the Hulkbuster armour called Veronica?
Chosen answer: This is a fairly US-centric gag. In Archie comics, the titular Archie has two competing love interests: Betty and Veronica. Given the Hulk/Banner's history with Betty Ross being able to calm him down, Tony Stark has named the containment system/Hulkbuster armor "Veronica".